We exploit the 1996 reform of the German child benefit program to identify the causal effect of child benefits on fertility. Generally, the reform increased child benefits. However, the exact amount of the increase varied by household income and sibship size. We use this heterogeneity of the reform to identify causal effects on fertility using a difference-in-differences setting. We apply the large samples of the German Mikrozensus and the rich data of the German Socioeconomic Panel (SOEP). The child benefit reform did not yield robust or statistically significant fertility effects for low income couples. We find some support for positive fertility effects for higher income couples deciding on a second birth.